In surface filtration, particles are captured at the surface of a filter membrane. The size of the captured particles is determined by the pores at or near the surface of the filter membrane.
There is little or no migration of dust into the matrix of the filter medium.
Surface filters comprising a top layer of powder particles such as metal powder particles are known in the art A top layer comprising metal particles is characterized by a low open area and consequently such a top layer may easily capture particles.
However, surface filters having a top layer of powder particles show a limited porosity and therefore a high pressure drop.